Method and apparatus for sterilizing articles

ABSTRACT

Method and apparatus for sterilizing articles including introducing the article and liquid solution into a collapsible pouch formed of vapor-impermeable sheet material, sealing the collapsible pouch to form a gas-tight assembly, and heating the gas-tight assembly to vaporize the liquid solution to produce an atmosphere of hot vapor. The liquid is introduced into the pouch in a quantity sufficient to create an overpressure when vaporized which is indicated by the collapsible pouch expanding to a distended condition. In one embodiment, the liquid solution is vaporized by irradiating the gas-tight assembly with microwave radiation. In other embodiments particularly suited for sterilizing a plurality of metallic articles, the at least one article is surrounded by shielding, which may be separate from or integrated with the pouch, which presents a barrier to the transmission of microwave radiation. The pouch containing the shielded article or articles and liquid solution is sealed and the gas-tight assembly is irradiated with microwave radiation to vaporize the liquid whereupon the article or articles are sterilized under the effect of vapor under pressure.

BACKGROUND OF THE INVENTION

This is a continuation of application Ser. No. 274,768 filed Nov. 22,1988, now U.S. Pat. No. 5,039,495, which is a continuation-in-part ofapplication Ser. No. 184,246 filed Apr. 21, 1988, now U.S. Pat. No.5,019,344.

This invention relates generally to methods and apparatus forsterilizing articles, such, for example, as dental and other medicalinstruments, such as dental handpieces.

The need for effective sterilization of dental instruments, such asdental handpieces, is more important today than ever before due to therealization of the significant potential for infection via dentalprocedures and the increase in the rate of transmission of seriousdiseases by blood and saliva. However, from a practical viewpoint, notonly must the sterilization procedure be effective, it must also berapid, i.e., have a short turn-around or cycle time. Thus, it will beunderstood that the quantity of any one instrument that a practitioneror institution must purchase and have available for use will depend onthe frequency of treatments requiring that instrument and on theturn-around time required to sterilize the instrument. In the case ofdental handpieces, which generally are required for most treatmentsperformed in the dental operatory, an extended sterilization cycle meansthat a larger inventory of available handpieces must be maintained. Thehigh cost of dental handpieces, on the other hand, often limits thenumber of available handpieces, which in turn may result in hasty andtherefore ineffective attempts at, or even dispensing with, lengthysterilization procedures. This of course is unacceptable.

Heat sterilization methods, such as steam heat (autoclave), dry heat,and chemical vapor, are generally preferred over cold immersion methods,which are generally not effective unless glutaraldehyde is used and theinstrument is immersed for 7-10 hours. Chemical vapor sterilization hasthe advantages of minimal corrosion of burs and other sharp instruments(steam sterilization or immersion in most liquid disinfectants producesdullness and rusting) and a cycle time which is relatively shortcompared to cold sterilization techniques.

One type of chemical vapor sterilizer which is in commercial use(available from MDT Corporation of Gardena, Calif. under the designationHarvey Chemiclave) comprises a sterilizer which uses moderate heat(about 270° F.), pressure (about 20 psi) and a special solution composedprimarily of 3A alcohol (about 80%) and water (about 9%) with smallamounts of acetone, ketone and formaldehyde. The sterilization time isabout 20 minutes after proper pressure is reached. The length of timerequired to reach pressure depends on the size of the load. On the otherhand, the purchase price of this arrangement is higher than steam anddry heat processors. Additional drawbacks are that relatively largequantities of sterilizing solution are required, and odor and minorirritation of eyes, nose and throat from chemical vapors oftenaccompanies use, the sterilizing chamber must be cleaned on a frequentbasis, the instruments should be wrapped to preserve sterility, and thesimultaneous sterilization of a plurality of instruments results in thepossibility of cross-contamination. Moreover, the sterilization cycletime, although less than the time required for the sterilization bysolution immersion, is still relatively long, essentially because of therelatively large chamber volume.

U.S. Pat. No. 4,400,357 issued Aug. 23, 1983 to Hohmann, discloses anarrangement for chemical vapor sterilization of articles, such as dentalhandpieces, which would appear to overcome some of the above-mentionedproblems. The patent discloses an arrangement in which the article to besterilized is situated in an enlarged portion of a rigid vessel. Aliquid reaction agent is charged into a narrow portion of the vesselwhich is in communication with the enlarged article-containing vesselportion. The liquid reaction agent is heated to produce a vapor whichflows into the first vessel portion to sterilize the article. The firstvessel portion may be designed to accept only a single article in whichcase the amount of liquid reaction agent required to generate the vaporis relatively small which in turn reduces the heating time required forvaporization and the overall sterilization cycle time. The patentsuggests that the means for heating the liquid reaction agent maycomprise a microwave radiator. In this case, the vessel is situated suchthat only the narrow liquid-containing vessel portion is subjected tothe microwave radiation while the article to be sterilized is keptoutside the radiation field which, the patent notes, avoids theformation of spark gaps at border surfaces and seams of the articlewhich cause surface destruction. In any event, although microwaveradiation is known to have beneficial sterilizing effects, the patentnotes that microwave radiation will not penetrate into the seams andcrevises of the article and not kill micro-organisms situated therein.Although possibly reducing the time required for sterilization, thearrangement proposed in the patent has various drawbacks which haveapparently prevented adoption and commercialization of this arrangement.For example, it requires a complicated, specially designed microwavegenerator adapted for positioning the vessel with only the liquidreaction agent-containing portion in the radiation field of themicrowave generator with the article-containing vessel portion outsidethe radiation field. It requires a specially designed rigid vessel whicheither must be cleaned after each use to avoid cross-contamination ordiscarded at significant expense. Moreover, the sterilizing effect ofthe microwave radiation is not utilized since the microwave energy isused only for vaporizing the liquid reaction agent.

A good discussion of the sterilization of articles, such as dentalinstruments, by microwave radiation is set forth in U.S. Pat. No.3,753,651 issued Aug. 21, 1973 to Boucher. Briefly, it is noted thatsterilization by microwave radiation is due to both thermal effects,such as microwave induced heat, and non-thermal effects, which thepatent suggests may affect a metabolic system distinct from that ofthermal energy. It is disclosed that improved surface sterilizationresults are obtained when the articles are subjected to microwaveradiation while situated in a humid atmosphere, i.e., an atmospherehaving a relative humidity of at least 50% or supersaturated with wateror saline solution. To this end, the articles to be sterilized areplaced on trays which are situated in a rigid, microwave-transparentcontainer having a known volume, along with a quantity of water orsaline solution determined by the container volume so as to besufficient when vaporized to increase the humidity of the atmospherewithin the container to the desired value. After placing the articles tobe sterilized and the water or saline solution into the container, thecontainer is sealed with a lid and then placed within the cavity of amicrowave generator and subjected to microwave radiation. Theelectro-magnetic energy penetrates through the container walls toevaporate the water or saline solution to produce the desired humidity,and at the same time, proceeds to sterilize the surface of the articleby the thermal and non-thermal effects discussed above. It is indicatedthat this procedure results in reduced cycle time for effectivesterilization compared to dry heat or steam sterilizing methods and thatthe localized arcing (sparking) which usually occurs when metallicobjects are irradiated by microwave radiation is practically eliminatedin the moist atmosphere.

The patent also points out that the container can be filled with any gasto constitute the atmosphere to be humidified. For example, it issuggested that a gas or vapor sterilant can be introduced into thecontainer through valves provided in the container walls to takeadvantage of their chemical sterilizing effects, although care should betaken to avoid heating the article being sterilized to a point where itreaches the ignition or explosion point of the gas.

The arrangement proposed in U.S. Pat. No. 3,753,651 has drawbacks whichhave apparently prevented it from being adopted on a practical basis.For example, as noted in the above-discussed U.S. Pat. No. 4,400,357,only surface sterilization is achieved by microwave irradiation andmicro-organisms present on surfaces located within the seams andcrevices of the article will not be killed, especially if blood andsalivary protein are deposited on those surfaces. Moveover, therelatively large volume of the container which is necessary toaccommodate the articles to be sterilized in turn requires a relativelylarge volume of water or saline solution to achieve the desiredhumidity. This results in an increase in the time required for theevaporation of the water or saline solution thereby increasing theoverall sterilization cycle time.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide new and improvedmethods and apparatus for sterilizing articles such as dental andmedical instruments, particularly dental handpieces.

Another object of the present invention is to provide new and improvedmethods and apparatus for vapor sterilization under pressure of sucharticles.

A further object of the present invention is to provide new and improvedmethods and apparatus for sterilizing one or more metallic articles,including dental instruments and instruments having sharp edges andpoints, in a microwave radiation field without sparking or arcing.

Yet another object of the present invention is to provide new andimproved methods and apparatus for effectively sterilizing articles,such as medical and dental articles, using simple, readily availablematerial and equipment and with a cycle time which is significantlyreduced relative to prior art arrangements.

Briefly, in accordance with the present invention, these and otherobjects are attained by providing an arrangement wherein an article tobe sterilized is situated within a collapsible pouch formed of flexiblesheet material which is vapor-impermeable. The collapsible pouch has anopening which permits insertion of the article into the pouch, theopening being sealable by the user to retain the article in the pouchand to prevent the loss of vapor therefrom. A predetermined quantity ofliquid solution is introduced into the pouch along with the articlewhereupon the opening is sealed to form a gas-tight assembly. The liquidis then heated by any suitable means until it vaporizes. In accordancewith the invention, the quantity of liquid solution introduced into thecollapsible pouch is sufficient so that upon vaporization, anoverpressure is created within the pouch. That the required overpressurehas been achieved is visually apparent according to the invention byobservation of the walls of the pouch during vaporization of the liquidsolution, the walls flexing outwardly from their initial collapsedcondition under the forces of the increasing internal pressure andreaching a fully distended condition upon the internal pressure reachingthe required overpressure. The hot vapor contacts the surfaces of thearticle under pressure penetrating into the narrow seams and crevicesthereof. The article is allowed to remain in the atmosphere of the hotvapor under pressure for a certain time whereupon it is effectivelysterilized.

In one embodiment of the invention, particularly suited for thesterilization of medical instruments such as dental handpieces, afterintroducing the handpiece and liquid solution into the pouch and sealingthe opening thereof, the thus-formed gas-tight assembly is placed withinthe cavity of a microwave radiator and subjected to microwaveirradiation. In this embodiment, the collapsible pouch is formed ofsheet material which, in addition to having the above-mentionedcharacteristics, is also transparent to microwaves. The liquid solutionis vaporized under the thermal effects of the microwave radiationproducing a hot sterilant vapor atmosphere under pressure as describedabove. At the same time, the handpiece is subjected to microwaveradiation. Sterilization of the handpiece is therefore achieved by thethermal and non-thermal effects of microwave radiation as well as byvapor under pressure. The combined microwave and vapor sterilizationachieves effective and complete sterilization of the dental handpiece insignificantly less time than has been possible heretofore. It isnoteworthy that, surprisingly, no arcing occurs, despite microwaveirradiation, in the course of sterilization of a single dental handpieceaccording to this procedure.

It is advantageous to utilize microwave energy for vaporizing the liquidsolution within the collapsible pouch in the vapor sterilizationtechnique of the invention due to efficiency and the ready availabilityof microwave generators. As described above, the sterilizing effects ofmicrowave irradiation and/or vapor under pressure can be utilized in thesterilizing of a single dental handpiece according to the inventionwithout the risk of arcing or sparking. However, it would not bepossible to sterilize a plurality of handpieces or other instrumentssituated within the same collapsible pouch in this manner withoutrisking the possibility of arcing or sparking. Indeed, vaporsterilization according to the invention of even a single pointedinstrument, such as a dental explorer, may result in arcing where theinstrument is subjected to microwave radiation used to heat and vaporizethe liquid solution in the gas-tight assembly.

In accordance with another aspect of the invention, the simultaneousvapor sterilization of a plurality of dental handpieces and/or one ormore pointed instruments, situated in the same collapsible pouch, can beaccomplished utilizing microwave energy to vaporize the liquid solutionand without the risk of arcing or sparking by substantially surroundingthe instrument or instruments by shielding means for preventing thetransmission of microwave radiation while maintaining the instrument orinstruments in communication with the ambient atmosphere. The pouchcontaining the shielded instruments and liquid is sealed to form agas-tight assembly whereupon the sterilization procedure may proceed bysubjecting the gas-tight assembly to microwave irradiation to producethe hot vapor as described above. The shielding means eliminates therisk of any sparking or arcing even for instruments having sharp pointsand edges. The hot vapor atmosphere under pressure communicates with theone or more instruments to sterilize the same.

The shielding means may include a holder member, separate from orintegrated with the pouch, defining an interior which is surrounded bymicrowave electromagnetic radiation shield material. The shielding meansmay also comprise a holder member which itself is formed of microwaveelectromagnetic radiation shield material. Alternatively, a portion ofthe area of the sheet material forming the collapsible pouch itself maybe provided with shielding so that the shielded area surrounds aninterior portion of the pouch which is thereby shielded from microwaveelectromagnetic radiation. The instruments to be sterilized are situatedwithin the shielded interior portion of the pouch while the liquidsolution is disposed in an unshielded interior portion to permitvaporization by microwave irradiation.

According to another aspect of the invention, the collapsible pouchpreferably is formed as the first step in the procedure from a sectionof an elongate tubular web of suitable plastic sheet material, e.g. apair of overlying sheets presealed along their outer edge margins, andusing suitable hot-wire sealing apparatus. In this manner, the size ofthe pouch can be "customized" for the geometry of the particular articlebeing sterilized.

DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the present invention and many of theattendant advantages thereof will be readily understood by reference tothe following detailed description when considered in connection withthe accompanying drawings in which:

FIG. 1 is an orthoganal view of apparatus in accordance with theinvention;

FIG. 2 is a sectional view taken along line 2--2 of FIG. 1 of a dentalhandpiece and liquid sterilant solution within a sealed collapsiblepouch forming a gas-tight assembly;

FIG. 3 is a sectional view of the gas-tight assembly shown in FIG. 2after vaporization of the liquid sterilant solution;

FIG. 4 is a perspective view of a roll of two-ply tubular web materialused for forming a collapsible pouch;

FIG. 5 is a perspective view of hot-wire sealing apparatus in useforming a collapsible pouch from the two-ply tubular web material shownin FIG. 3;

FIG. 6 is a top plan view of a pouch-forming section of the two-plytubular web material, one side of which has been sealed and into theopening of which a dental handpiece and liquid sterilant solution havebeen introduced;

FIG. 7 is a perspective view of one embodiment of shielding means inaccordance with the invention;

FIG. 8 is a sectional view of a gas-tight assembly including acollapsible pouch containing liquid sterilant solution and the shieldingmeans surrounding a plurality of instruments to be sterilized;

FIG. 9 is a sectional view taken along line 9--9 of FIG. 8;

FIG. 10 is an exploded perspective view of a second embodiment ofshielding means in accordance with the invention surrounding a pluralityof instruments to be sterilized;

FIG. 11 is a partial sectional view of a first modification of theshielding means shown in FIG. 10;

FIG. 12 is a partial sectional view of a second modification of theshielding means shown in FIG. 10;

FIG. 13 is a partial sectional view of a third modification of theshielding means shown in FIG. 10;

FIG. 14 is a sectional view of a gas-tight assembly including acollapsible pouch containing liquid sterilant solution and the shieldingmeans shown in FIG. 10 surrounding a plurality of instruments to besterilized;

FIG. 15 is a perspective view of a third embodiment of shielding meansin accordance with the invention surrounding a plurality of instrumentsto be sterilized;

FIG. 16 is a sectional view of a gas-tight assembly including acollapsible pouch containing liquid sterilant solution and the shieldingmeans shown in FIG. 15 surrounding a plurality of instruments to besterilized;

FIG. 17 is a perspective view of a fourth embodiment of shielding meansin accordance with the invention surrounding an instrument to besterilized;

FIG. 18a is a sectional view of an embodiment wherein the shieldingmeans illustrated in FIG. 17 is integrated with a collapsible pouch andillustrating the insertion of an instrument to be sterilizedsimultaneously into both the shielding means and pouch;

FIG. 18b is a view similar to FIG. 18a illustrating a gas-tight assemblyformed after the instrument is fully inserted and the pouch sealed;

FIG. 19 is a top plan view of a gas-tight assembly including acollapsible pouch wherein shielding is provided on the sheet materialforming the pouch; and

FIG. 20 is a front elevation view of another embodiment of apparatus inaccordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings wherein like reference charactersdesignate identical or corresponding parts throughout the several views,and more particularly to FIGS. 1-3, apparatus in accordance with theinvention, generally designated 10, comprises a microwave generator,similar to conventional microwave ovens and schematically shown at 12,having a rotating table 14 located within the microwave cavity 16. Adental handpiece 18 to be sterilized is situated within a sealed,flexible or collapsible pouch 20 along with a predetermined quantity ofliquid solution 22 to form a gas-tight assembly 24. The collapsiblepouch 20 is designed with minimal volume preferably sufficient toaccommodate only a single dental handpiece and is formed of sheetmaterial which is transparent to microwave radiation and impermeable tothe vapor of the liquid solution. In a preferred embodiment, the liquidsolution comprises 2 ml. of glutaraldehyde solution and the pouch 20 isformed of sheet material having a thickness of about 2 mils andcomprising a laminate of polyester and polyethylene. A predeterminedamount of liquid solution 22 is introduced through an opening into thepouch 20 along with the dental handpiece 18 whereupon the opening issealed to form the gas-tight assembly 24. The gas-tight assembly 24comprising the collapsible pouch in which the dental handpiece 18 andliquid solution 22 is placed on the rotating table 14 within the cavity16 of microwave generator 12 and subjected to microwave irradiation. Asthe microwave radiation continues, the liquid solution 22 is vaporizedunder the thermal effects of the microwave radiation producing a hotvapor. In accordance with the invention the quantity of liquidintroduced into the collapsible pouch is sufficient so that uponvaporization, an overpressure is created within the pouch 20. That therequired overpressure has been achieved is visually apparent accordingto the invention by observation of the walls 26 of pouch 20 which flexoutwardly from their initially collapsed condition (FIG. 2) under theforces of the increasing internal pressure and reach a fully distendedcondition, designated 26' in FIG. 3, upon the internal pressure reachingthe minimum or lower overpressure requirement. The hot vapor contactsthe surfaces of the dental handpiece 18 under pressure penetrating intothe narrow seams and crevices thereof. At the same time, the dentalhandpiece 18 is subjected to microwave irradiation. The microwaveirradiation is continued for a certain time with the dental handpiece inthe radiation field and in the atmosphere of the hot vapor underpressure until the handpiece has been sterilized. Sterilization of thehandpiece 18 may therefore be achieved by the thermal and non-thermaleffects of the microwave radiation as well as by hot vapor underpressure.

Tests using a conventional, commercially available 500 watt microwaveoven and the arrangement described above have shown that a dentalhandpiece, contaminated with bacterial spores, in particular spores ofBacillus-Stearothermophilus, was effectively sterilized, i.e., all ofthe spores were killed, in only five minutes. It will be appreciatedthat spores of this bacillus are extremely difficult to kill and aregenerally used to test sterility effectiveness of steam autoclaves. Noarcing or sparking of the handpiece caused by microwave radiation wasobserved when the handpiece was so irradiated in the atmosphere of thehot vapor under pressure.

The rotating table 14 is utilized in order to obtain a uniformirradiation of the gas-tight assembly 24. Of course, this can bedispensed with if the particular microwave radiator employed provides auniform radiation field within the cavity.

It is desirable to minimize the volume of the collapsible pouch 20 toreduce sterilization cycle time. Since different articles to besterilized have different geometries, a preferred construction of pouch20 will permit a "custom design" by the practitioner or his staff for aparticular instrument for minimizing the internal volume of thegas-tight assembly. In this connection, referring to FIGS. 4-6, thepouch 20 is formed from 2-ply web material 28 of constant width,preferably maintained and made available to the practitioner in the formof a roll 30. The web material 28 comprises a pair of overlying elongatesheets of polyester-polyethylene laminate whose outer edge margins 38have been previously sealed to each other to form a tubularconstruction. A section 34 of the tubular web material 28 is cut fromroll 30 along the line 36, the section having a length L which issomewhat greater than that required to accommodate the instrument,namely, the dental handpiece 18, to be sterilized. One of the open ends38 of the web material section 34 is sealed by fusing the overlyingsheets to each other along a transverse seal line 40 by a hot-wiresealing apparatus 42 (FIG. 5). The seal apparatus 42 comprises a fixed,heated resistance wire 44 mounted on and extending across a housing 46and a counter-member 48 formed of a rubber-type material fixed to acover member 50 pivotally connected to housing 46 in a position so as tocome into registering alignment with wire 44 when cover member 50 ispivoted to its closed position. A series of transversly alignedperforations 52 are formed through the sealed outer edge margins 32 ofthe web 28 and pair of locating pegs 54 spaced from each other by adistance equal to the distance between each pair of transversely alignedperforations 52 are provided in front of resistance wire 44.

The construction of the gas-tight unit 24 proceeds as follows. Aftercutting tubular web section 34 from roll 30, a pair of transverselyaligned perforations 52 proximate to end 38 are located over the pegs 54such that an end region of the tubular web section 34 overlies theheated resistance wire 44. The cover member 50 of apparatus 42 is closedwhereby the counter-member 48 urges the overlying sheets of tubular web28 against each other and against the heated resistance wire 44whereupon the sheets are fused to each other to form the transverse sealline 40 and thereby the collapsible pouch 20. The dental handpiece 18and about 2 ml of liquid glutaraldehyde solution 22 are introduced intopouch 20 through opening 56. The opening 56 is then sealed using thehot-wire sealing apparatus 42 in the same manner as described above toform a second transverse seal line 58 (shown in phantom in FIG. 6)proximate to the end 60 of section 34 thereby forming the sealed,gas-tight assembly 24.

The above described arrangement for constructing the gas-tight assembly24 is advantageous in that it is simple and fast. Moreover, the volumeof the gas-tight assembly is custom designed for the particularinstrument being sterilized, on the one hand, being sufficient toaccommodate the instrument, and on the other hand, being minimized tothe extent possible to reduce the quantity of liquid sterilant solutionrequired to achieve the desired internal overpressure upon vaporization,and in turn to decrease the amount of time required to vaporize theliquid sterilant solution, and, therefore, the overall sterilizationcycle time. The equipment required for constructing the collapsiblepouch is simple, inexpensive and readily available. The pouches aredisposable after the sterilization treatment has been completed and thedental handpiece can be stored in the gas-tight assembly until its useis required. The sterilization treatment is odorless and does not causeirritation of the eyes, nose or throat. The microwave cavity 16 need notbe cleaned since the vapor is contained within the gas-tight assembly24. Importantly, the instrument 18 is completely sterilized in a veryshort time.

It is advantageous to utilize microwave energy for vaporizing the liquidsolution within the collapsible pouch in the vapor sterilizationtechnique of the invention because of the efficiency of its thermaleffects and the ready availability of microwave generators. However,although arcing is not a problem in the combined microwave and vaporsterilization of a single dental handpiece, as described above, it wouldnot normally be possible to simultaneously sterilize a plurality ofinstruments situated in the same collapsible pouch or even a singleinstrument having a sharp point or edge in the manner described aboveusing microwave energy to vaporize the liquid solution in the gas-tightassembly without risking the potential for arcing or sparking to occur.

In accordance with another aspect of the invention, referring to FIGS.7-18, arrangements are illustrated by which a simultaneous vaporsterilization of a plurality of instruments 62 situated in the samecollapsible pouch 20 is accomplished utilizing microwave energy tovaporize the liquid sterilant solution 22 without the risk of arcing orsparking. In the case of the arrangements shown in FIGS. 7-17, theinstruments to be sterilized are substantially surrounded by shieldingmeans which present a barrier to the transmission of microwaveelectromagnetic radiation. The instruments surrounded by the shieldingmeans are introduced into the collapsible pouch with the liquidsolution. The pouch is sealed and the gas-tight assembly is irradiatedwith microwave radiation to vaporize the liquid to produce a vaporatmosphere at an appropriate overpressure indicated by the pouchobtaining its distended configuration. The shielding means providecommunication between the instruments and the ambient atmosphere so thatthe instruments are bathed in the vaporized liquid atmosphere underpressure to effectively sterilize them by vapor under pressure. Theinstruments are on the other hand shielded from the microwave radiationby the shielding means to eliminate the possibility of arcing orsparking.

Referring to FIGS. 7-9, the shielding means 64 (FIG. 7) includes aholder member 66 comprising a tubular receptacle formed of anelectrically insulative material, such as plastic, having a plurality ofapertures 67 formed therethrough, and microwave electromagneticradiation shield material 68 covering the outer surface of the holdermember. Shield material 68 may comprise, for example, a double layeredknitted mesh of tin-copper-steel wire which presents a barrier to thetransmission of microwave radiation and which is available in strip formfrom the Tecknit Company of Cranford, N.J. under the designation EMCShielding Tape. Thus, in this embodiment, the shielding means 64 has atubular shape and comprises the apertured tubular holder member 66 overthe outer surface of which a strip or strips of the knitted wire mesh 68is wrapped.

In use, the instruments 62 are initially surrounded by shielding means64 by inserting them into the interior of the tubular holder member 66whereupon the shielding means and instruments surrounded thereby areintroduced into a collapsible pouch 20 along with a quantity of liquidsterilant solution 22 whereupon the pouch is sealed to form a gas-tightassembly 24 as described above. The gas-tight assembly is irradiated bymicrowave radiation whereupon the liquid solution is vaporized by thethermal effects of the microwave radiation and the hot vapor underpressure flows through the mesh and apertures 67 of tubular holdermember 66 into contact with the surfaces of the instruments 62 tosterilize the same. No sparking or arcing occurs.

Referring to FIGS. 10-12, another embodiment of shielding means,designated 100, includes a holder member 102 comprising a rigidbox-shaped receptacle formed, for example, of plastic material, andhaving a removeable cover 106. Apertures 108 are formed through thewalls of the receptacle 102 and cover 106. The outer surfaces of theholder member are covered by microwave electromagnetic radiation shieldmaterial 110 of the type described above, as best seen in FIG. 12. Inuse, instruments 112 to be sterilized are surrounded by shielding means100 by situating them within the receptacle 102 within locating notchesprovided by upstanding shelves 114 and positioning the cover 106 toclose the receptacle so that the instruments are surrounded by theshield material 110. The shielding means 100 and instruments 112surrounded thereby are introduced into a collapsible pouch 20 with aquantity of liquid sterilant 22 whereupon the pouch is sealed to form agas-tight assembly 24. The gas-tight assembly is irradiated by microwaveradiation to vaporize the sterilant solution and the hot vapor underpressure flows through the mesh of shield material 110 and apertures 108of receptacle 102 and cover 106 to sterilize the instruments. Theinstruments 112 are shielded from the microwave radiation to eliminatethe possibility of arcing or sparking. The size of the receptacle 102,although not critical, preferably is as small as possible so that it canbe accommodated within a collapsible pouch the volume of which is inturn sufficiently small so that the quantity of sterilant solutionrequired to produce the pressurized atmosphere is correspondinglyminimized. In this manner, sterilization cycle time is reduced.

The shield material 110 may be applied over the outer surfaces of thewalls of the receptacle 102 and cover 106 as shown in FIG. 11 or,alternatively, may be applied over the inner surfaces of the receptaclewalls as seen in FIG. 12, or embedded within the thickness of thereceptacle walls as seen in FIG. 13.

It will be understood that the holder member 102 may be formed ofmaterials other than plastic and the shield material may comprisematerials other than wire mesh. For example, the holder member 102 ofshielding means 100 shown in FIG. 10 may comprise a box-shapedreceptacle formed of paper or board material having a metallic coatingprovided on its outer surface. This construction is advantageous in thatit is sufficiently inexpensive in manufacture as to be disposable afteruse.

Referring to FIGS. 15 and 16, another embodiment of shielding means,designated 120, comprises a holder member 122 which is itself formed ofshield material, such as the knitted wire mesh shield material describedabove. Holder member 122 comprises a sheath of mesh shield materialhaving one end 124 which is closed and an insertion end 126 which isclosable upon insertion of one or more instruments 128 into the interiorof the holder member. In use, instruments 128 are surrounded byshielding means 120 by inserting them into the sheath of holder member122 through the insertion end 126 which is then closed by crimping. Theshielding means 120 surrounding instruments 128 is then introduced intoa collapsible pouch 20 with a quantity of liquid whereupon the pouch issealed to form a gas-tight assembly 24. The solution is vaporized byirradiating the gas-tight assembly 24 with microwave radiation and thehot chemical vapor under pressure flows through the mesh of the holdermember to sterilize the instruments. The instruments are themselvesshielded from the microwave radiation to eliminate the possibility ofarcing or sparking.

Referring now to FIG. 17, another embodiment of shielding means,designated 130, also comprises a holder member 132 in the form of asheath which is itself formed of shield material. In particular, theholder member 132 is formed of a metallic foil material, such asaluminum foil, having an open insertion end 134. The metal foil hasperforations 136 formed therethrough to provide communication betweenthe interior of the holder member 132 and the ambient atmosphere. Theshielding means 130 is used in essentially the same manner as describedabove. At least one instrument 138 to be sterilized is surrounded by theshielding means 130 by inserting it into the holder member 132 throughthe insertion end 134 thereof which is then closed by crimping. Theshielding means 130 surrounding instrument 138 is introduced into acollapsible pouch along with liquid sterilant solution. Sterilizationproceeds as described above.

It is understood that the holder member 132 may be formed of shieldmaterials other than as described above. For example, the holder membermay be formed of plastic film or paper provided with a metallic coatingor a metallic laminate. It is also noted that the perforations 136should be of a size less than a certain dimension to ensure thatmicrowave radiation cannot pass through them. For example, if theperforations are circular and have diameters less than about one-quarterthe wavelength of the microwave radiation, the radiation should forpractical purposes be substantially prevented from passing through them.

Referring now to FIGS. 18a and 18b, an embodiment of the invention isshown wherein shielding means are integrated with a collapsible pouch toform a unitary assembly. More particularly, shielding means in the formof a sheath-like holder member 160 are situated within the interior of acollapsible pouch 162 of the type described above and affixed to theinner surface thereof such as by adhesive tacking at 164. Holder member160 is formed of a metallized substrate, such as aluminized paper, andhas substantially the same construction as that shown in FIG. 17including perforations 166 and an open insertion end 168. The holdermember 160 is fixed within the pouch 162 in a position such that theopen insertion end is situated adjacent to and recessed a small distanceinwardly from the open end 170 of pouch 162. A capsule or sachet 172containing an appropriate quantity of liquid solution is alsopredisposed within pouch 162.

In use, referring to FIG. 18a, an instrument 174 to be sterilized isinserted into pouch 162 through its open end 170 and, at the same time,into the interior of the holder member 160 of the shielding meansthrough the insertion end 168. The insertion end of holder member 168 isclosed and pouch 162 is sealed to form a gas-tight assembly 176 shown inFIG. 18b. At this time the liquid solution 178 is released from sachet172 whereupon the assembly 176 is irradiated with microwaveelectromagnetic radiation to vaporize the liquid.

The assembly comprising the collapsible pouch 162 and holder member 160fixed thereto may advantageously be constructed and sold as a singleunit, either with or without the sachet of liquid sterilant solutionpredisposed therein. The assembly is preferably constructed so as to bedisposable after a single use.

A somewhat different construction of an embodiment wherein shieldingmeans are integrated with a collapsible pouch is illustrated in FIG. 19.In this embodiment, a defined portion S of the area of the sheetmaterial of a collapsible pouch 20A of the type described above isprovided with microwave electromagnetic radiation shield means while theremaining area NS of the sheet material of pouch 20A remains transparentto microwave radiation. The shield means may take the form of a metallicgrid-like coating 142 deposited over the area S of the sheet material ofthe pouch as shown or may simply comprise a continuous or solid metalliccoating. The shielded area S surrounds an interior portion of thecollapsible pouch which is thereby shielded from microwave radiationwhile the non-shielded area NS surrounds an interior portion of thepouch which is not so shielded. A transversely extending series ofspaced heat seals 144 join opposed regions of the sheet material ofpouch 20A to separate the shielded interior portion of pouch 20A fromthe non-shielded interior portion. The shielded and non-shieldedinterior portions communicate with each other through the voids betweenthe heat seals 144. The shielded interior portion of pouch 20A is ofsufficient extent to surround instruments 146 to be sterilized.

In use, the instruments 146 are inserted into the shielded interiorportion of pouch 20A through a first open end which is then sealed at148. Liquid solution, preferably contained within a cup 150, isintroduced into the non-shielded interior portion of pouch 20A through asecond open end which is then sealed at 152 to form a gas-tightassembly, designated 24A. The gas-tight assembly is irradiated withmicrowave radiation whereby the solution in cup 150 vaporizes and thepressurized vapor atmosphere fills the shielded interior portion of thepouch to sterilize instruments 146. The possibility of arcing orsparking is eliminated since the shielding 142 presents a barrier to thetransmission of the radiation into the interior portion of the pouch inwhich the instruments are situated. It will be understood that it is notessential that the pouch be provided with seals 144 or that the liquidbe contained within a cup so long as the instruments are substantiallysurrounded by shield means and the liquid sterilant is situated in anon-shielded interior portion of the pouch.

It will be understood that sterilization can be accomplished accordingto the invention using only the vapor under pressure arrangement of theinvention in the absence of microwave radiation. For example, referringto FIG. 19, the gas-tight assembly 24 of FIG. 2, including a collapsiblepouch in the interior of which is sealed an instrument to be sterilizedand an appropriate quantity of liquid sterilant solution, is situated inthe interior of an infrared radiator device 86 in which a rod-shapedinfrared radiator 88 is provided. Elliptical mirrors 90 are providedwithin the infrared radiator device 86 defining a pair of vocal linesfor the infrared radiation emitted from radiator 88. The infraredradiator 88 is positioned on the first focal line and the gas-tightassembly is situated in a simple holder device 92 at the second focalline. When the radiator 88 is activated, a high beam concentration ofthe infrared radiation is focused onto the gas-tight assembly 24 rapidlyvaporizing the liquid solution to sterilize the instrument by chemicalvapor as described above.

Obviously, numerous modifications and variations of the presentinvention are possible in the light of the above teachings. It istherefore to be understood that within the scope of the claims appendedhereto, the invention may be practiced otherwise than as specificallydisclosed herein.

What is claimed is:
 1. A method for sterilizing at least one article byvapor under pressure comprising the steps of:providing an expandablepouch formed of flexible, vapor-impermeable sheet material, saidexpandable pouch existing in a collapsed condition in its normal stateand having the ability to expand to a visually apparent substantiallydistended condition; introducing at least one article to be sterilizedinto said pouch while said pouch is in said collapsed condition;introducing a quantity of liquid into said pouch while said pouch is insaid collapsed condition, said quantity of liquid being sufficient sothat when said pouch is sealed to form a gas-tight assembly and saidliquid is vaporized, an over-pressure is created within said pouch whichwill expand said pouch to said visually apparent substantially distendedcondition; sealing said pouch to form a gas-tight assembly; vaporizingsaid liquid to produce an atmosphere of hot vapor under pressure in saidgas-tight assembly so that said pouch expands from said collapsedcondition to said visually apparent substantially distended conditionunder the effect of said pressure; and verifying that an atmosphere ofhot vapor under pressure exists in said gas-tight assembly by utilizingthe expansion of said pouch as an indication thereof; whereby said atleast one article situated within said gas-tight assembly is sterilizedunder the effect of vapor under pressure.
 2. The method recited in claim1 wherein said step of vaporizing said liquid comprises irradiating saidgas-tight assembly with radiation.
 3. The method recited in claim 2wherein said radiation comprises microwave radiation, and including theadditional step of shielding said at least one article in its entiretyfrom said radiation during said vaporizing step.
 4. The method recitedin claim 1 including the preliminary step of constructing an expandablepouch by forming a section of a tubular web from a pair of overlyingsheets of plastic material sealed at their longitudinal edge margins;and sealing one of the ends of said tubular web section by fusing firstnarrow transversely extending regions of said overlying sheets proximateto said one of said ends to each other.
 5. The method recited in claim 1wherein said expandable pouch is formed of plastic sheet material andsaid step of sealing said pouch opening to form a gas-tight assemblycomprises the step of fusing narrow transversely extending regions ofoverlying portions of said pouch to each other.
 6. The method recited inclaim 1 wherein said expandable pouch has an interior volume sufficientto accommodate only a single article to be sterilized.